1. Field of Invention
This invention relates generally to apparatus adapted to determine the degree to which the physical stability of a patient is impaired, and more particularly to a dynamic system including a computer for this purpose which is responsive to shifts in the weight of a patient standing on an unsteady platform to provide measurements from which are derived a stability index useful in deciding how then to treat the patient so as to improve his condition.
2. Status of Prior Art
The concern of this invention is with the physical balance or stability of a human subject and the degree to which his balance is impaired and therefore requires corrective treatment appropriate to the subject's condition. Whether considered in mechanical terms or in the context of human physical behavior, stability is that property of a body which causes it to develop forces opposing any position or motion-disturbing influence. Stability therefore depends on being able to reach a state of equilibrium or balance.
An individual whose physical stability is impaired is then predisposed to falling down. The human body incorporates a complex balance-control mechanism, and any imbalance therein, regardless of its origin, leads to falling and this may have serious consequences.
The present invention resides in a dynamic system adapted to determine by means of an unsteady platform on which the subject being tested stands and a computer associated therewith, the degree to which the stability of the subject is disturbed. The stability index yielded by the system makes it possible to then decide on the nature of the treatment appropriate to the subject's condition. (In the specification, the terms "subject" and "patient" are used interchangeably.)
The Kellogg International Work Group defines a fall as "an event which results in a person coming to rest inadvertently on the ground or other lower level, other than as a consequence of the following: sustaining a violent blow; loss of consciousness; sudden onset of paralysis, as in a stroke; or an epileptic seizure." A fall resulting from impaired stability lies within this definition, for the individual falls only because he is unable to maintain his balance.
As revealed by the available statistics, fatal falls in the United States often occur in elderly individuals, the mortality rate due to falls rising markedly with advancing age. Each year, a significant percentage of those individuals over 75 years of age who are brought to hospital emergency rooms are there because of a fall-related injury. And about 70% of general injury treatment in hospital emergency rooms in this age group is imputed to falling accidents.
Many senior individuals exhibit a proclivity for falling due to any number of neuromusculoskeletal dysfunctions. Brittle bones combined with slower reflexes result in bone breakage and other associated injuries and these are enormously expensive to repair. Several factors including age or sex are involved in identifying high-risk individuals, the probability of falling increasing exponentially with advancing age. Women appear to be at higher risk in most age groups.
Another risk factor is osteoporosis which decreases bone resistance to mechanical injury, thereby increasing the risk of compression fractures. This then predisposes certain bones (hip, pelvis, forearm, vertebrae) to possible fracture. It is generally recognized that chronic diseases causing cardiovascular and neuromuscular dysfunction can significantly increase the risk of falling. Other factors also contribute to falls, such as gait and balance disturbances, poor vision, a disturbed mental state, and the use of medication or alcohol.
To prevent falls or to reduce their possibility, it is known to use screening techniques to identify high-risk individuals. Once a high-risk individual is identified, steps can then be taken to remove or minimize risk factors, such as by strengthening weak muscles or altering a drug regimen to avoid side effects resulting in a loss of balance. But an effective and reliable technique to screen such high-risk individuals has not heretofore been realized.
Thus numerous bio-mechanical techniques have been developed to analyze balance, but these have largely been static tests lacking components of dynamic response, or they were aimed at neuromuscular analysis and therefore not practical for screening. These and other previously known tests fail to take into account the matter of function; i.e., the physical abilities a subject actually needs in order to carry out daily activity. A static test, such as posturography, determines the amount of sway a subject exhibits when the subject is standing with his eyes open or closed. Such posturography tests have also evolved into a pseudo-functional test in which a subject stands on a static (non-moving) platform and shifts his weight in performing certain motor tasks while a computer monitors the results. Such motor tasks are similar to tracking a target, or using body sway to cause a video cursor to travel around a video "racetrack."
A known modification of pseudo-functional static testing is the incorporation therein of a bio-mechanical test using a force platform which pivots under the ankle and can slide front-to-back. This arrangement enables the researcher to induce sway and thereby determine the degree to which the subject can compensate by changing his posture.
These known testing techniques all suffer from a major flaw, for they are not really functional assessments. Since instability resulting in falls occurs during imbalance while walking (not standing still), in order to be effective a functional test must determine the ability of the subject to maintain balance during the performance of a task requiring body motion. Moreover, static or pseudo-functional balance testing is only effective for initial screening, in that patients gradually adopt a posture for control strategy after becoming familiar with the test conditions. Quantitative measures of adaptive abilities are therefore needed to make testing of equilibrium more useful clinically.
In equilibrium control, two information processes enable the subject to stand and walk over a variety of surfaces and conditions. There is redundant information supplied by sensory modalities related to orientation, these being somatosensory, vestibular and visual, all three having different frames of reference. There is also weighted information whereby the system modifies the relative importance of these inputs. However, under abnormal physiological conditions, such as when the subject suffers from a disease, either the inputs are disturbed or the weighted information may not be suitable for effective control of equilibrium.
As a consequence, compensation for the balance p deficit may require another adaptive strategy. Indeed, it is the ability of a subject to modify balance strategy for proper equilibrium in response to various environmental challenges that makes quantitative assessments difficult. It is therefore necessary to utilize a system for equilibrium testing that incorporates a variety of support surface conditions that influence the vestibular system and the somatosensory input, yet simultaneously relies on a variety of visual conditions, all successively imposed on the subject being tested. A dynamic system in accordance with the invention does just that, and enables quantification of the subject's responses under such varied conditions.
Of prior art interest is the stability test disclosed in the article by Lord et al. "Exercise Effect on Dynamic Stability in Older Women" published in Arch. Phys, Med. Rehabit. Vol. 77 March 1996 in which a subject being tested is coupled to a recording pen movable on an undulating track.
Also of prior art interest as showing platforms supported by elastic members on which a patient stands during testing, which elastic members generate a reactive restoring force to the supported platform which is proportional to the magnitude of deflections from equilibrium are the following patents:
______________________________________ Heurte 5,360,015 (11/94) Wallace et al. 4,463,946 (8/84) McFarland 3,826,145 (7/74) Roost 5,186,062 (2/93) ______________________________________
In the above-identified co-pending application Ser. No. 08/685,951 there is disclosed a dynamic system adapted to test a patient to determine the degree to which his physical stability is impaired. The system includes a stable platform yielding signals that depend on the magnitude and direction of the force applied to the platform face. The platform is rendered unsteady by a convex rocker dish resting on the face of the platform and having a flat top on which the patient stands. The resultant signals which are a function of the orientation of the flat top of the dish relative to the platform face are fed to a computer whose output is applied to a video monitor having a display screen on which is presented a cursor which position is controlled by the signals.
The standing patient, while viewing the screen, is required to so shift his weight on the rocker dish as to alter the orientation of the flat top to produce signals causing the cursor to travel from the center of the screen toward a computer-generated target presented on one corner of the screen and to then acquire the target. The computer measures and scores the time it takes for the patient to cause the cursor to acquire the target as well as other variables that reflect the relative stability of the patient. These scores, taken together, define a stability index useful in deciding how then to treat the patient to improve his condition.
In the dynamic system disclosed in the above-identified Zanakis copending patent application Ser. No. 08/685,951, mounted below the stable platform is a transducer responsive to the force applied to the face of this platform by a convex rocker dish resting on this face. When the patient to be tested stands on the flat top of the convex dish, the signals then generated by the transducer are a function of the direction and magnitude of the applied force along three mutually-perpendicular axes of movement (X-Y-Z). Hence these signals depend not only on how the standing patient shifts his weight on the dish to alter the orientation of the flat top of the dish relative to the horizontal plane, but the signals are also a function of the patient's body weight. Hence a heavy patient produces transducer signals of greater magnitude than a lighter patient.
In the copending application, Ser. No. 08/761,683 other embodiments are disclosed of an unsteady platform to test the degree to which a patient exhibits physical instability. In one of these embodiments, the unsteady platform takes the form of a circular disc placed within a gimbal and hinged thereto, the gimbal being disposed within a circular opening in a base plate and being hinged to that plate.
In another embodiment, the unsteady platform takes the form of a disc anchored on a hemispherical ball rotatable within a socket, the ball and socket forming a universal joint whereby the platform may be tilted in any direction.
In testing for instability, a patient standing on the unsteady platform is required to shift his weight and therefore his center of gravity, this action causing the platform to tilt.
In each of the unsteady platforms disclosed in the earlier filed Zanakis applications, the platform is free to tilt and its tilt away from the horizontal plane normally occupied by the platform is not restrained or dampened.
Some patients being tested on the unsteady platform may have great difficulty in maintaining their balance. Thus if a patient's stability is grossly impaired, and the patient shifts his weight to tilt the platform, in doing so the patient may pitch off the platform. While security rails are provided which the patient may grasp if he feels the need to steady himself, some patients feel highly insecure when standing on a platform whose freedom to lilt is unrestrained.